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Math Revolution GMAT Instructor V
Joined: 16 Aug 2015
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GMAT 1: 760 Q51 V42 GPA: 3.82
John traveled the entire 50 km trip. If he travelled the first 20 km o  [#permalink]

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Difficulty:   5% (low)

Question Stats: 93% (01:30) correct 7% (01:22) wrong based on 94 sessions

### HideShow timer Statistics [GMAT math practice question]

John traveled the entire 50 km trip. If he traveled the first 20 km of the trip at a constant rate 40 km per hour and the remaining trip at a constant rate 20 km per hour, what is his average speed, in km per hour?

A. 20 km/h
B. 23 km/h
C. 25 km/h
D. 26 km/h
E. 27 km/h

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Re: John traveled the entire 50 km trip. If he travelled the first 20 km o  [#permalink]

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MathRevolution wrote:
[GMAT math practice question]

John traveled the entire 50 km trip. If he traveled the first 20 km of the trip at a constant rate 40 km per hour and the remaining trip at a constant rate 20 km per hour, what is his average speed, in km per hour?

A. 20 km/h
B. 23 km/h
C. 25 km/h
D. 26 km/h
E. 27 km/h

If John travels 20 km at 40 km/hr he would take $$\frac{1}{2}$$ hour.
The remainder of the trip - 30 km was traveled at 20 km/hr and took a time of $$\frac{30}{20} = \frac{3}{2}$$ hours.

The total time taken is 2 hours and the distance traveled is 50 km.
Therefore, the average speed at which John travels is $$\frac{50}{2} = 25$$km/h (Option C)

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Re: John traveled the entire 50 km trip. If he travelled the first 20 km o  [#permalink]

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MathRevolution wrote:
[GMAT math practice question]

John traveled the entire 50 km trip. If he traveled the first 20 km of the trip at a constant rate 40 km per hour and the remaining trip at a constant rate 20 km per hour, what is his average speed, in km per hour?

A. 20 km/h
B. 23 km/h
C. 25 km/h
D. 26 km/h
E. 27 km/h

Average speed = total distance/total travel time

total distance = 50 km

total travel time = time spent driving at 40 kmh + time spent driving at 20 kmh
time = distance/speed
So, time spent driving at 40 kmh = 20/40 = 1/2 hour
And time spent driving at 20 kmh = 30/20 = 3/2 hours
So, TOTAL travel time = 1/2 + 3/2 = 4/2 = 2 hours

Average speed = 50/2 = 25 kmh

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Re: John traveled the entire 50 km trip. If he travelled the first 20 km o  [#permalink]

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MathRevolution wrote:
[GMAT math practice question]

John traveled the entire 50 km trip. If he traveled the first 20 km of the trip at a constant rate 40 km per hour and the remaining trip at a constant rate 20 km per hour, what is his average speed, in km per hour?

A. 20 km/h
B. 23 km/h
C. 25 km/h
D. 26 km/h
E. 27 km/h

Average Speed= Total distance traveled/Total time taken
=50/(20/40+30/20)
=50/2=25
Math Revolution GMAT Instructor V
Joined: 16 Aug 2015
Posts: 7599
GMAT 1: 760 Q51 V42 GPA: 3.82
Re: John traveled the entire 50 km trip. If he travelled the first 20 km o  [#permalink]

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=>
Ave Speed = ( Total Distance ) / ( Total Time )
The total distance = $$50 km$$.
Total time is $$\frac{20}{40} + \frac{30}{20} = 0.5 + 1.5 = 2$$
The average speed is $$\frac{50}{2} = 25.$$

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Joined: 15 Oct 2016
Posts: 29
Re: John traveled the entire 50 km trip. If he travelled the first 20 km o  [#permalink]

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MathRevolution wrote:
[GMAT math practice question]

John traveled the entire 50 km trip. If he traveled the first 20 km of the trip at a constant rate 40 km per hour and the remaining trip at a constant rate 20 km per hour, what is his average speed, in km per hour?

A. 20 km/h
B. 23 km/h
C. 25 km/h
D. 26 km/h
E. 27 km/h

Average speed = total distance / total time = 50 / (20/40 + 30/20) = 50 / (1/2 + 3/2) = 25
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Re: John traveled the entire 50 km trip. If he travelled the first 20 km o  [#permalink]

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MathRevolution wrote:
[GMAT math practice question]

John traveled the entire 50 km trip. If he traveled the first 20 km of the trip at a constant rate 40 km per hour and the remaining trip at a constant rate 20 km per hour, what is his average speed, in km per hour?

A. 20 km/h
B. 23 km/h
C. 25 km/h
D. 26 km/h
E. 27 km/h

Time for travelling first 20 Kms = 0.50 Hr
Time for travelling first 30 Kms = 1.50 Hr

Total time taken = 2.00 Hrs

So, Average speed in kmph is $$\frac{50}{2} = 25kmph$$, Answer must be (C)
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Re: John traveled the entire 50 km trip. If he travelled the first 20 km o  [#permalink]

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MathRevolution wrote:
[GMAT math practice question]

John traveled the entire 50 km trip. If he traveled the first 20 km of the trip at a constant rate 40 km per hour and the remaining trip at a constant rate 20 km per hour, what is his average speed, in km per hour?

A. 20 km/h
B. 23 km/h
C. 25 km/h
D. 26 km/h
E. 27 km/h

We can use the equation: average = total distance/total time

50/(20/40+ 30/20)

50/(1/2 + 3/2)

50/(4/2) = 50/2 = 25

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